California began regulating vehicle emissions within its boundaries before the Environmental Protection Agency was even a gleam in President Richard Nixon's eye.

Since that agency was founded in 1971 with an executive order by Nixon, the state has retained the right to set its own—more stringent—emission rules.

Now, under President Donald Trump and climate-science denier Scott Pruitt, who runs the EPA, there's widespread fear that the agency will attack the "waiver" it granted to California that permits its zero-emission vehicle sales requirements.

That could happen, though it would be a major court battle that might last the entire remainder of Trump's first four-year presidential term.

But, according to Don Anair, who's the research and deputy director of the Clean Vehicles Program at the Union of Concerned Scientists, it may not happen yet.

He explained why in an interview with Green Car Reports.

President Donald Trump (Photo courtesy DoD)

But first, some history. California's separate rules first became truly costly for automakers in the mid-1990s, with the state's first round of zero-emission vehicle requirements.

They led most notably to the famous GM EV1 electric car, but the cost of compliance and installation of infrastructure—plus some considerable political maneuvering we're not going to get into—meant that the first ZEV mandate was dialed back a few years later.

When the state decided to regulate not only "criteria emission" (carbon monoxide, nitrogen oxides, and hydrocarbons) but also the climate-change gas carbon dioxide, the challenge for automakers became even tougher.

Because a car's CO2 emissions are directly proportional to the fuel it burns, California was in essence setting its own fuel-economy rules, separate from the U.S. rules issued by the NHTSA.

The EPA under President George W. Bush fought the idea that it should regulate CO2 on a national basis, and the conflict went all the way to the Supreme Court.

Once the Court ruled that not only could the EPA regulate CO2 emissions, it had to, then the EPA and NHTSA had to coordinate their standards—and, even more challenging, give the powerful California Air Resources Board a seat at the negotiating table.

President Obama inspects the 2011 Chevrolet Volt

That all happened in a rush, because with the Bush EPA having slow-walked issuing any regulations for 2012 and later model-year vehicles, President Barack Obama was inaugurated in January 2009 less than two years before 2012 model-year cars could go on sale in January 2011.

Automakers must commit hundreds of millions of dollars to investments in technology and tooling, years ahead of time, based on the regulations they will have to meet.

The lack of understanding of what fuel-economy and emission standards would be required made them deeply unsettled, and Obama convened panels to set the 2012 through 2017 standards as a first order of business.

In the end, the stiffer California standards more or less became the national standards, both for the 2012-2017 rules adopted in 2010 and a second set covering 2018 through 2025 vehicles that were signed into law in 2012.

That second set included a "midterm review," in which the EPA would look at the cost and success of the earlier standards and assess whether the final set (for 2022 through 2025) should be kept or altered.

Last summer, a report issued by the EPA concluded that automakers had successfully met the 2012-2017 standards, at lower cost than projected.

Golden Gate Bridge, connecting San Francisco and Marin County, California

Based on hundreds of pages of expert testimony and analyses, the agency concluded that the final set of standards would be achievable. Those rules were adopted by the EPA just days before Donald Trump was inaugurated.

The howling from automakers and their lobbyists was immediate: they accused the agency of rushing its decision, since the original schedule permitted the review to go as late as spring of 2018.

The comment period for the 2022-2025 regulations was reopened in March.

Anair suggests that this is where it will get interesting.

National Plug-In Day 2012: San Francisco, with 60 Nissan Leafs in front of the Golden Gate Bridge

Automakers plan to bring comments noting a years-long change in the makeup of the vehicles they sell, with passenger sedans and hatchbacks falling dramatically and light trucks of all sorts—particularly crossover utility vehicles—soaring.

The latter are heavier and less aerodynamic than the former, meaning they use more fuel. Hence, manufacturers say, it will be harder to meet the emission limits on CO2 than expected when the rules were written in 2012.

The process of revising EPA rules requires any decisions to be based on evidence, data, and reputable scientific analysis.

What the automakers bring to the table in that regard, and how they position their expectations for their product lineups by 2025, Anair said, may indicate how hard they'll fight the California ZEV mandate that's permitted by the state's waiver.

"It's a positive sign that the Administration has reached out to California Governor Jerry Brown to participate in the Midterm Review," he commented.

California Air Resources Board chair Mary Nichols (via Twitter)

The state's Air Resources Board and the EPA both participated in the voluminous Technical Assessment Report issued last summer, Anair pointed out, which led to the rules that were finalized in January.

It will be interesting to see "what new evidence they bring to the table over the next several months that isn't already part of the existing record," he said.

Automakers, Anair suggested, "want to avoid a fight with California," which is by far their largest single market in the U.S.

If a new set of standards through 2025 is proposed by the EPA, he said, whether California signs off on them or chooses to stick with its existing set—which it reaffirmed in March that it plans to do—may bear on whether the EPA chooses to target its waiver.

In other words, that could well happen, but probably not immediately.

For electric-car owners and advocates, then, the process of revisiting the 2022-2025 emission limits bears close watching.

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